<!DOCTYPE html>
<html lang="en">
<head>
    <meta charset="UTF-8">
    <meta name="viewport" content="width=device-width, initial-scale=1.0">
    <meta http-equiv="X-UA-Compatible" content="ie=edge">
    <title>Document</title>
</head>
<body>
    <ul>
        <li>1</li>
        <li>2</li>
        <li>3</li>
    </ul>
    <script>
        // 输出：3,3,3
        // var add_the_handlers = function (nodes) {
        //     var i;
        //     for (i = 0; i < nodes.length; i += 1) {
        //         nodes[i].onclick = function (e) {
        //             console.log(i);
        //         };
        //     }
        // };
        // 输出：0,1,2
        var add_the_handlers = function (nodes) {
            var helper = function (i) {
                return function (e) {
                    console.log(i);
                };
            };
            var i;
            for (i = 0; i < nodes.length; i += 1) {
                nodes[i].onclick = helper(i);
            }
        };
        var lis = document.getElementsByTagName('li');
        // console.log(lis);
        add_the_handlers(lis);
    </script>
</body>
</html>